Data carriers according to the invention are in particular security or value documents, such as bank notes, identity cards, passports, visa stickers, check forms, shares, certificates, postage stamps, air tickets and the like, as well as labels, seals, packages, or other elements for product protection. The simplifying designation “data carrier” and “security or value document” will therefore hereinafter always include documents of the stated type.
Such papers whose market value or utility far exceeds the value of the material require suitable measures to make them recognizable as authentic and distinguishable from imitations and forgeries. They are therefore provided with special security elements which are ideally not, or only with great effort, imitable and not falsifiable.
In the past particularly those security elements have proved useful that can be identified and recognized as authentic by the viewer without aids but are simultaneously only producible with extremely great effort. These are e.g. motifs produced by intaglio printing, which are characterized by their typical tactility easily recognizable even to the layman, and cannot be imitated with other common printing processes or by copy machines.
Line or intaglio printing, in particular steel intaglio printing, is an important technique for printing data carriers, in particular papers of value, such as bank notes and the like.
Intaglio printing is characterized by engraving or etching depressions into the printing plates to produce a printed image. The ink-transferring areas of the printing plate are thus present as depressions in the printing plate surface.
Before the actual printing operation, ink of pasty consistency is applied to the engraved printing plate and surplus printing ink removed from the surface of the printing plate by means of a wiping blade or wiping cylinder, so that ink remains only in the depressions. Then a substrate, as a rule paper, is pressed against the printing plate and thus also into the ink-filled depressions of the printing plate, and removed again, whereby ink is drawn out of the depressions of the printing plate, sticks to the substrate surface and forms a printed image there. If transparent inks are used, the thickness of inking determines the shade. A light shade is thus obtained when a white data carrier is printed with small ink layer thicknesses, and darker shades when it is printed with thick ink layers. The ink layer thickness is in turn dependent to some degree on the engraving depth.
Intaglio printing allows relatively thick inking on a data carrier in comparison with other common printing methods such as offset printing. The comparatively thick ink layer produced by intaglio printing, together with the partial deformation of the paper surface resulting from the paper being pressed into the engraving of the printing plate, is easily palpable manually even to the layman and thus also readily recognizable as an authenticity feature by its tactility. The tactility cannot be imitated with a copy machine, so that line intaglio printing offers high-quality protection against forgeries.
However, these printed images show signs of wear particularly in documents, such as bank notes and identification documents, that are exposed to strong mechanical and chemical loads, and are moreover openly accessible to tampering.
To increase falsification security, in particular of identification documents such as passports, one page of the passport bearing the personal data to be specially protected, such as name, date of birth, photo, signature, etc., is therefore usually provided with a transparent foil structure printed partly on the inner side, so that said data are not directly accessible. The production of such a passport is described for example in EP 0 364 730 A2.
In such foil-coated documents the data are no longer accessible to direct access from outside, but they are also no longer tactilely perceptible if executed by intaglio printing.